Fabrication of metallic microstructures via exposure of photosensitive composition

ABSTRACT

A method of forming microstructures. An article including a metal atom precursor is disproportionally exposed to electromagnetic radiation in an amount and intensity sufficient to convert some of the precursor to elemental metal. Additional conductive material may then be deposited onto the elemental metal to produce a microstructure.

RELATED APPLICATIONS

[0001] This application is a divisional of U.S. Ser. No. 09/755,645,filed Jan. 5, 2001 which claims the benefit under 35 U.S.C. §119(e) ofU.S. S.No. 60/175,068, filed Jan. 7, 2000.

STATEMENT AS TO POTENTIAL RIGHTS UNDER FEDERALLY SPONSORED RESEARCH ANDDEVELOPMENT

[0002] Research leading to the invention disclosed and claimed hereinwas supported by DARPA and the National Science Foundation (NSF)(ECS-9729405). This work used MRSEC shared facilities supported by theNSF (DMR-9400396 and DMR-9809363). The U.S. Government may have certainrights to the invention.

FIELD OF THE INVENTION

[0003] This invention relates to methods for forming a conductivepattern using photographic film.

BACKGROUND OF THE INVENTION

[0004] A multitude of techniques for shaping (such as stamping,grinding, and milling) and joining (such as welding and mechanicaljoining) metals are highly developed for the fabrication of macroscopicstructures. Application of these techniques to the fabrication andassembly of metallic microstructures (structures having features <100μm) becomes increasingly difficult as the feature sizes become smaller.For that reason, new approaches to microfabrication that are not derivedfrom fabrication techniques used on a large scale have been developed. Awidely used technique for fabrication of metallic microstructures ismicroelectrodeposition of metals on an appropriately shaped mandrel ortemplate. Two examples of this class of processes are through-maskelectroplating and LIGA (Lithographie, Galvanoformung, Abformung), bothof which are based on projection photolithography (for LIGA, commonlycarried out using x-rays, although the availability of the SU-8 class ofphotoresist has reduced the need for x-ray exposure in making thickstructures). Although these methods provide ways to form metallicmicrostructures, they are processes with several steps, and requirefacilities of limited availability.

[0005] Recently, methods for the microfabrication of metallic, 2D and 3Dstructures based on the combination of soft lithography andmicroelectrodeposition have been described, the latter both through amask of photoresist and onto patterned, conducting surfaces. Thepattern-transfer step in these soft lithographic techniques typicallyuses an elastomeric stamp with a surface relief structure that carriesthe desired pattern. These stamps are usually formed by moldingpolydimethylsiloxane (PDMS) against a ‘master’ composed of a reliefpattern in photoresist, and obtained by photolithography. These mastersmay be generated using a technique based on high-resolution commercialprinting and high-resolution optical reduction. This procedure isefficient: from design, through stamp, to initial structure typicallyrequires no more than 24 hours. Both the preparation of the mask and thegeneration of the master by photolithography may require access tospecialized devices and facilities (i.e., high-resolution image setters,clean rooms) that are more readily available than the mask-makingfacilities required in high-resolution photolithography, but that arestill not available to every laboratory that might benefit from mediumresolution microfabrication.

SUMMARY OF THE INVENTION

[0006] The present invention provides a method for producing metallicand other conductive microstructures. The microstructures may beproduced on a substrate, for example, a planar substrate such asphotographic film, and may subsequently be removed from the substrate.The microstructures may be produced in a short amount of time and mayuse equipment readily available to those skilled in the art.

[0007] In one aspect, a method is provided in which a conductive patternis formed. An article including a metal atom precursor capable ofconversion to elemental metal is provided and a first portion of thearticle is disproportionately exposed to electromagnetic radiation at alevel greater than at a second portion of the article. The article isexposed in an amount and for a period of time sufficient to convert atleast some of the precursor at one of the portions to elemental metal ata conversion level greater than conversion of precursor to elementalmetal at the other portion. Then, a metal is deposited from a sourceexternal of the metal atom precursor, proximate the portion of thearticle including metal atom precursor converted at a greater conversionlevel in an amount greater than deposition of metal at the otherportion.

[0008] In another aspect, the invention provides for a method thatincludes deforming a flexible metal structure from a first configurationto a second configuration and depositing auxiliary metal on the metalstructure to the extent that the structure is self-supporting in thesecond configuration.

[0009] In another aspect, the invention provides for a method thatincludes exposing photoresist to electromagnetic radiation through ametal mask, developing the photoresist to form a photoresist pattern,directing a metal deposition composition to the metal mask via thephotoresist pattern, and depositing auxiliary metal on the metal mask.

[0010] In another aspect, the invention provides for a method of forminga conductive pattern. A photographic film is illuminated with a desiredillumination configuration, and the film is developed so thatilluminated or non-illuminated portions of the film are adjusted to bein an altered state. Additional conductive material is selectivelydeposited onto portions of the film in an altered state in amountsgreater than amounts of conductive material deposited on portions of thefilm not in the altered state.

[0011] In another aspect, the invention provides for a method of forminga discontinuous metallic structure. A photographic film is illuminatedwith a desired structure configuration and the film is developed so thatilluminated or non-illuminated portions of the film are adjusted to bein an altered state. Additional conductive material is selectivelydeposited onto portions of the film in an altered state in amountsgreater than amounts of conductive material deposited on portions of thefilm not in the altered state.

[0012] Other advantages, novel features, and objects of the inventionwill become apparent from the following detailed description of theinvention when considered in conjunction with the accompanying drawings,which are schematic and which are not intended to be drawn to scale. Inthe figures, each identical or nearly identical component that isillustrated in various figures is represented by a single numeral. Forpurposes of clarity, not every component is labeled in every figure, noris every component of each embodiment of the invention shown whereillustration is not necessary to allow those of ordinary skill in theart to understand the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

[0013]FIG. 1 provides a schematic flow chart illustrating one embodimentof the invention.

[0014]FIG. 2 provides a photocopy of three optical micrographs (a, b andc) showing three successive stages in the production of a microstructuredeveloped using an embodiment of the invention. Each of FIGS. 2a, 2 band 2 c also includes a photocopy of a micrograph of each stage atgreater magnification.

[0015]FIG. 3a provides a photocopy of an optical micrograph showing aserpentine gold wire produced using an embodiment of the invention aswell as an oblique view of the edge of the same wire.

[0016]FIG. 3b provides a graph providing results for electricalresistance at different contact points along the gold wire of FIG. 3a.

[0017]FIGS. 4a-4 c illustrate three different schematic views of amicrofluidic system produced by an embodiment of the invention.

[0018]FIG. 4a illustrates a starting design as printed on paper.

[0019]FIG. 4b illustrates a three dimensional perspective view of amicrofluidic system.

[0020]FIG. 4c provides a photocopy of an optical micrograph of the threeelectrodes of the microfluidic system of FIG. 4b.

[0021]FIG. 4d provides the results of a cyclic voltammogram obtainedusing the microfluidic system shown in FIGS. 4b and 4 c.

[0022]FIGS. 5a-5 c provide a photocopy of three optical micrographs thatschematically illustrate the stepwise assembly of a three-circle openspherical structure using an embodiment of the invention.

[0023]FIGS. 6a-6 b provide a schematic illustration (6 a) and an opticalmicrograph (6 b) that illustrate the formation of a curved metallicstructure from a planar metallic structure using an embodiment of theinvention.

[0024]FIGS. 7a-7 c provide a photocopy of three optical micrographsillustrating the formation of discontinuous metallic structures on asingle substrate.

[0025]FIG. 8a provides a schematic illustration of an embodiment of theinvention used to produce a free standing metallic structure.

[0026]FIG. 8b provides a photocopy of an optical micrograph of ametallic structure produced by the method illustrated in FIG. 8a.

DETAILED DESCRIPTION

[0027] The invention provides a method for forming a pattern ofconductive material on a planar or non-planar substrate. The substratemay include a chemical composition that can be altered by illuminationwith electromagnetic radiation. The substrate may be flexible or rigid.Preferably, the substrate includes a photosensitive composition, such asthat included in a photographic or other photosensitive film. Thephotosensitive composition can include any type of photosensitivecomposition having suitable properties, such as a metal atom precursoror other material that changes state in response to exposure (ornon-exposure) to electromagnetic radiation and possible subsequentdevelopment, and facilitates subsequent selective deposition of aconductive material onto or away from material areas experiencing thestate change.

[0028] In one aspect of the invention, a photographic film is exposed toan illumination configuration having a desired pattern. For example, thephotographic film can be standard black and white or color 35 mmphotographic negative film, black and white or color slide (i.e.,positive) film, large format photographic film, instant black and whiteor color film, black and white or color print paper, etc. Thephotographic film may be exposed to the illumination configuration invarious ways, including using the film in a standard photographic camerato image a desired pattern, directing a beam or multiple beams ofillumination, e.g., a laser beam, to illuminate desired portions of thephotographic film, placing the film in sufficiently close proximity to adisplay device (such as a CRT display, electroluminescent (EL) display,a back-lit LCD, etc.) that displays a desired pattern and thereforeilluminates the photographic film with the desired pattern, etc. Thus,desired portions of the photographic film can be disproportionatelyexposed to electromagnetic radiation at a level greater than otherportions of the film. When exposing the photographic film using astandard photographic camera, the film can image a printed hard copy ofa pattern, such as a circuit pattern printed or drawn onto a papersubstrate, for example, by a computer-aided design (CAD) application andassociated printer, or the film can image an actual sample of thepattern, such as an actual circuit board pattern. When exposing the filmusing a scanned illumination beam or other display, a CAD image file orother image data can be used to drive the illumination beam scanner,display or other device so that the film is exposed to the desiredillumination configuration pattern.

[0029] Exposing the substrate, e.g., photographic film, to the desiredillumination configuration causes illuminated or non-illuminatedportions of the photographic composition to be adjusted into an alteredstate, i.e., experience a physical or chemical change. For example, if aphotosensitive composition including a metal atom precursor, such asthat in conventional silver halide photographic film, is used, exposure(or non-exposure) of the metal atom precursor to electromagneticradiation (and possible subsequent development) can cause the precursorto change to an altered state, such as an elemental metal. Thus, ifconventional silver halide photographic slide film is exposed to adesired illumination configuration, relatively darker or non-illuminatedportions of the film will experience a chemical change such that silverparticles (elemental silver), or grains, are formed in a higher densityat low-level or non-illuminated portions of the film compared to filmportions exposed to a higher level of illumination. In most photographicfilms, the physical or chemical change results after the film is exposedto illumination and developed using conventional development techniques.However, the physical or chemical change in the illuminated ornon-illuminated film portions can occur simultaneously with exposure orshortly thereafter without requiring conventional photographicdevelopment. For example, when using instant photographic films,development occurs shortly after the film is exposed to illumination anddoes not require an additional development step. Both the exposure timeand the illumination intensity are typically equal to those used instandard photographic processes and are known to those skilled in theart. When substrates other than photographic film are used, exposuretimes and illumination intensities can be routinely determined.

[0030] After the substrate is exposed to an illumination configuration,the illuminated or non-illuminated portions may be augmented, or furtherdeveloped, by depositing a metal or other conductive materialselectively on the illuminated or non-illuminated portions (portionsexperiencing or not experiencing a state change). For example, whenusing conventional silver halide photographic slide film,non-illuminated portions of the developed film can be further augmentedusing an electroless deposition of elemental silver such that thedeposited silver is catalyzed by the silver grains in the photographicfilm to selectively increase the silver grain size in the film at thenon-illuminated portions. Thus, further development or augmenting of thefilm can result in an electrically continuous pattern in portions of thefilm, i.e., individual silver grains in the film are selectively grownso that the grains in illuminated or non-illuminated portions contacteach other or otherwise interact so as to form an electricallyconductive structure on the portion. A metal is deposited in an amountsufficient to provide conductivity to a portion when the portion onwhich the metal is deposited becomes conductive between one end of theportion and an opposing end of the portion. Once a portion of the filmbecomes conductive, this portion of the film can be additionally plated,for example by using electrochemical deposition of a metal or otherconductive material onto the augmented film portions. This additionaldeposition step can increase the width and/or thickness of the augmentedportions, if desired. The result may be an electrically conductivepattern that matches, or nearly matches, the pattern of the illuminationconfiguration used to expose the photographic film. The electricallyconductive pattern can be used for testing, prototyping, actual fielduse, for use as a mask in photolithographic processing, etc.

[0031] As described below in one example of the invention, a pattern ofsilver particles embedded in the gelatin matrix of exposed and developedsilver halide-based photographic film can serve as a template in abroadly applicable method for the microfabrication of metallicstructures or microstructures. In this exemplary method, a CAD file orportion of a CAD file is reproduced, or approximately reproduced, in thephotographic film by exposure and developing. In this example, theresulting pattern of discontinuous silver grains is developed, i.e.,augmented and made electrically continuous, by electroless deposition ofsilver, and the electrically continuous structure is then used as thecathode for electrochemical deposition of an additional layer of thesame or different metal or other conductive material. The overallprocess can be completed within 2 hours, starting from a CAD file, andcan generate structures with the smallest dimension in the plane of thefilm of ˜30 μm. Structures with an aspect ratio of up to five can alsobe obtained by using the metallic structures as photomasks inphotolithography using a photo resist, such as SU-8 photoresist, on thetop of the electroplated pattern, and exposed from the bottom, followedby development and electroplating through the patterned photoresist.This method of fabrication uses readily available equipment, and makesit possible to prototype a wide variety of metallic structures anddevices. The resulting structures—either supported on the film backing,or freed from it and possibly mounted on another substrate—areappropriate for use as passive, structural materials such as wire framesor meshes, as electric circuits and in microfluidic, microanalytical,and microelectromechanical systems (MEMS).

[0032] The method of microfabrication described below enables rapidprototyping of metallic microstructures with planar dimensions ≧30 μm. Asingle, continuous structure or two or more discontinuous structures maybe produced on a single substrate. Production of discontinuousstructures may, therefore, be performed simultaneously. An advantage ofthe described procedure is that laboratories with no access tosophisticated facilities for writing the masks required forphotolithography can carry out microfabrication at feature sizes usefulin a range of applications such as, for example: microfluidic systems,cell biology, microanalytical systems, microsensor, andmicroelectromechanical systems (MEMS).

[0033] One example of a pattern fabrication process involves five steps:i) printing of a design embedded in a CAD file on paper using ahigh-quality (e.g., 600 dots per inch, or greater, dpi printer; ii)photographic reduction of this print onto a silver halide-basedphotographic film using a commercial slide maker; iii) development ofthe exposed film; iv) electroless deposition of silver metal directly onthe exposed, developed film—that is, the finished slide—to make at leastportions of the pattern electrically continuous; and v) optionalelectrochemical deposition of metal or other electroactive or conductivematerial onto the silver to form or reinforce the final pattern. Thismethod can be especially useful in the fabrication of metallicmicrostructures for use in prototyping devices, and in applications—3Dfabrication, fabrication with unfamiliar materials—where conventionalprojection photolithography is difficult to apply or inapplicable.

[0034] One aspect of the invention uses a readily available photographicfilm recorder—a commercial slide (transparency) maker—that reproducesthe pattern of a CAD file—printed on paper with an officeprinter—directly onto silver halide-based photographic film.Alternatively, an image may be transferred directly from a CAD file tofilm using software and hardware known to those skilled in the art. Thepattern of silver particles in the developed photographic film, afterelectroless deposition to make the structure electrically conductive,serves as a template for electrochemical deposition of additional metal,and generates metallic microstructures. The entire procedure, fromreproduction of the CAD file onto photographic film to completion of thefinal metallic structure(s) can easily be finished within 2 hours anduses readily available equipment. This procedure makes it possible forvirtually all laboratories to generate a variety of useful metallicstructures with small planar feature sizes, for example, 30 μm.

[0035] The single step of the simple photographic reproduction of a CAD,or other, file onto a silver halide-based film can replace the multiple(partly photolithographic) steps in microcontact printing and LIGA forthe fabrication of appropriately shaped mandrels formicroelectrodeposition. The complete procedure from CAD-file to metallicstructure can easily be completed within two hours if instant film isused. Any photo camera or slide maker that accepts silver halide-basedor other suitable photographic film may be sufficient for thereproduction of the CAD file pattern. Structures with thickness smallerthan 2 μm may be porous due to the gelatin network. Higher resolution inthe width of the structures can be obtained using more professionalphotographic equipment. It is believed that the intrinsic limit ofresolution for this technique lies with the quality of the photographicequipment and is limited by aberrations of the optical elements, and notby the size of the grains in the film (<100 nm). The maximum size of astructure—or an array of structures—is limited by the size of the filmused, typically 35 mm×22 mm. Larger size silver halide-based film isavailable (up to 300 mm×400 mm).

[0036] The following describes a specific, exemplary method of theinvention and experimental results. However, as discussed above, theinvention is not limited to this specific example in which a desiredpattern is first printed using a computer-drawing (CAD) and the printedpattern is imaged onto a silver halide photographic film. Rather, othertypes of substrates, such as photographic films, imaging methods and/orconductive material augmentation processes can be used. For example, anactual micro circuit device could be used to image a frame ofphotographic film, i.e., one could “take a picture” of an actualmicrocircuit device and use the imaged photographic film to prepare aconductive circuit pattern by developing the film using conventionalphotographic techniques and further developing or augmenting the filmusing electroless plating, electro plating, or other selectivedeposition of conductive materials onto desired portions of the film.

EXAMPLES

[0037] Polagraph 35 mm instant black and white slide film (PolaroidCorporation; Cambridge, Mass.) was used as an article presenting metalatom precursors. Halo-Chrome™ silver electroless plating solution(Rockland Colloid Corp; Piermont, N.Y.), Tech 25 E gold plating solution(Technic Inc.; Providence, R.I.), Tech nickel plating solution (TechnicInc.; Providence, R.I.), Polydimethylsiloxane (Sylgard 184; Dow Corning,N.Y.), and SU-8 photoresist (Microchem Co.; Newton, Mass.) were used asreceived. NiSO₄.6H₂O (99%), NH₃.H₂O (29.8%), Na₂H₂PO₂.H₂O (>99%),Ru(NH₃)₆Cl₃ (>99%), NaCl (>99%), HCl (1N), Na₂S₂O₃ (>99%), K₃Fe(CN)₆(>99%) K₄Fe(CN)₆ (99%), and propylene glycol methyl ether acetate(PGMEA) were obtained from Aldrich. A black and white slide maker wasbought from Polaroid (Model IPC-2). The scanning electron micrograph(SEM) was done on a LEO digital scanning electron microscope, model 982and the cyclic voltammetry measurements were performed on a AFCB1Bipotentiostat (Pine Instrument Company; Grove City, Pa.).

[0038] Test patterns were designed using Freehand™ software (AdobeSystems Inc.) and printed on paper using a 600 dpi printer. The printedimages were reduced in size on slide films using the black and whiteslide maker. The contrast was set in the medium contrast mode and theexposure time was ˜0.5 second. The slide film was developed using thedeveloping package for Polagraph 35 mm slide film. The developed filmwas put in the silver electroless plating solution for about 15 minutes,then the desired metal was electroplated onto the patterns of silver.

Example 1

[0039]FIG. 1 illustrates an exemplary procedure used to fabricatemetallic microstructures using silver halide-based photographic film.One element in this film is a substrate 110, a polyester backing(typically ˜100 μm thick) covered with a gelatin layer 120 (typically ˜2μm thick) that contains silver halide. (Keller, K. Science andTechnology of Photography; VCH: Weinheim, German, 1993.) A CAD file wasfirst printed (130) on paper 135 with a 600 dpi office printer. Acommercial slide maker was then used to reproduce (150) the black andwhite image on the silver halide-based photographic film 140. Theinitially developed film leaves the silver particles 160 isolated, withno electrically continuous path connecting adjacent portions in thepattern. Electroless deposition of additional silver, catalyzed by thesesilver grains, increased the grain size so that the grains come intocontact 170. (Bjelkhagen, H. I. Silver-Halide Recording Materials forHolography and Their Processing; Springer-Verlag: New York, 1995 andZhang, Y.; Yan, T.; Yu, S.; Zhuang, S. Journal of the ElectrochemicalSociety 1999, 146, 1270.) At that point, all portions of the patternimage become electrically conducting (provided, of course, that theoriginal design was continuous). Subsequent electroplating using thisimage as the cathode provided metal structures that had the mechanicalstrength or optical density required for further applications.Freestanding metallic microstructures 180 can be obtained by dissolutionof the gelatin matrix in which the metallic structures are embedded. Dueto the high permeability of the gelatin layer (˜2 μm thick),(Bjelkhagen, H. I. Silver-Halide Recording Materials for Holography andTheir Processing; Springer-Verlag: New York, 1995,) the metal wasdeposited from both the side and the top onto the silver structuresduring the initial electroplating process. Once the upper surface of themetal grew out of the gelatin layer, the speed of deposition on the topof the metal structure was higher than on the side due to mass transportlimitations to delivering metal ions to the sides of the structures, orwithin the gelatin film.

Example 2

[0040]FIG. 2 shows optical micrographs of metallic lines (˜30 μm wide)generated by each of the steps in the fabrication process describedabove in Example 1. After development of the photographic image andbefore electroless deposition (FIG. 2a), the primary pattern of silverhalide grains had a line width of ˜25 ∞m and an edge roughness of ˜2 μm.After electroless plating (FIG. 2b), the line width increased to ˜26 μmand the edge roughness remained approximately the same. Afterelectroplating (FIG. 2c), a line width of ˜30 μm and an edge roughnessof ˜3 μm were observed. The limited optics of the slide maker resultedin distorted, incomplete reproduction of patterns with smaller features.The edge roughness of patterns printed on the paper also contributed tothe resolution of the final pattern, but it was not the major factor.The smallest feature sizes of metallic structures obtained using amaster pattern printed with a 3387 dpi high-resolution image-setter werestill ˜30 μm, with edge roughness of ˜3 μm. FIG. 2 also shows scanningelectron micrographs of the microstructure of the line patterns in thedifferent stages of the fabrication process. The growth and fusion ofsilver particles upon electroless plating and electroplating are clearlyvisible.

Example 3

[0041]FIG. 3a shows a gold serpentine wire (˜50 μm wide and ˜2.5 μmthick; total length of ˜648 mm) fabricated to test the electricalcontinuity of metallic structures made using this procedure as describedin Example 1. A uniform resistivity of ˜7×10⁻⁸ Ωm (FIG. 3b) was measuredover the full length of the wire, which is ˜3.5 times higher than thevalue reported for pure bulk gold (˜2×10⁻⁸ Ωm). (Lide, D. R. CRCHandbook of Chemistry and Physics; CRC Press: New York, 1999.) Aresidual gelatin network, or a network of grain boundaries still presentinside the wires after electroplating, are possible explanations forthis difference.

Example 4

[0042] A three-electrode system was fabricated using the proceduredescribed above and is illustrated in FIG. 4. FIG. 4a illustrates thedesign of the system on paper prior to reducing the size of the systemand transferring it to film. The electrodes are represented on paper bylines 410, 420 and 450, and their contact pads by structures 412, 422and 452 (40 mm×40 mm). The electrodes (FIGS. 4b and 4 c) weredifferentiated into two sets by selective electroplating: two wires, 490and 492, and their contact pads, 494 and 496, (5 mm×5 mm) were coveredwith gold (for the working and counter electrodes, 430 and 440,respectively) and one wire 482 and corresponding contact pad 484 (5 mm×5mm) with silver (for the reference electrode 460). The polyester base474 in the film enabled the use of this three-electrode structure in amicrofluidic device by placing a polydimethylsiloxane (PDMS) membrane470 having an inlet 476 and an outlet 478 with a channel 480 embossed inits surface directly on this structure (FIG. 4b and 4 c). The PDMSmembrane was made by casting PDMS against an SU-8 master. (Xia, Y.;Whitesides, G. M. Agnew. Chem. Int. Ed Engl. 1998, 37, 550.)

[0043] Cyclic voltammetry (FIG. 4d) of a solution containing Ru(NH₃)₆Cl₃demonstrated the performance of this three-electrode system. Thesolutions were injected into the channel using a single-use syringeconnected to the inlet with a piece of polyethylene tubing. The systemwas treated with a 0.1N HCl solution for about one minute prior to theelectrochemical measurements. The concentration of oxygen in allsolution was reduced by bubbling Ar gas through for at least 5 minutes.

Example 5

[0044] The solubility of a gelatin base in DMF or hot water allows forthe fabrication of freestanding structures. (Bjelkhagen, H. I.Silver-Halide Recording Materials for Holography and Their Processing;Springer-Verlag: New York, 1995.) The conditions required for releaseare sufficiently gentle that even fragile structures are not damaged.FIG. 5 shows sequentially, in FIGS. 5a, 5 b and 5 c, the construction ofa 3D structure, an open sphere, assembled from pieces that have beenfabricated using the technique described in Example 1. The line width ofeach of the nickel circles was ˜1 mm and their thickness was ˜50 μm.This example illustrates an alternative approach to rapid fabrication ofelements for 3D structures/MEMS.

Example 6

[0045] Flexible substrates, such as photographic film, make it possibleto fabricate topologically complex microstructures. FIG. 6(b) shows anickel serpentine wire (˜2 μm thick, and ˜100 μm wide) fabricated byelectroplating on a folded silver halide film. The film was exposed in aplanar orientation (FIG. 6a) and folded prior to electroless depositionand subsequent electroplating.

Example 7

[0046] The procedure described above works well to make continuousmetallic structures. During the fabrication of discontinuous structures,there is no continuous electrical pathway joining all the elements ofthe pattern, and therefore it is less practical to use electroplating.An electroless Ni plating solution (2.6 g NiSO₄.6H₂O, 5 ml NH₃.H₂O, and3.6 g Na₂H₂PO₂.H₂O in 200 ml H₂O) was used to build a thick Ni layer onthe patterned silver particles (continuous or discontinuous). FIG. 7ashows a “Veritas” logo consisting of a ˜2 μm nickel layer depositedusing electroless plating alone. FIGS. 7b and 7 c illustrate magnifiedportions of FIG. 7a to show detail of the continuous individualstructures obtained on a single substrate without the use ofelectroplating.

Example 8

[0047] The structures fabricated above all have relatively low aspectratios (height width), typically less than 0.1. FIG. 8 shows a procedurefor the fabrication of structures with a high aspect ratio. First, thefilm carrying the low aspect ratio structure was used both as thesubstrate and the mask in a photolithographic step. The photoresist 810was exposed to UV light from below the structure/mask 820 layer.Subsequent use of the photoresist pattern as the mask to directelectrodeposition of metals while using the original, low aspect ratiostructure as the cathode resulted in high aspect ratio structures. Thehigh aspect structures were produced as follows:

[0048] Electroplated film was produced as outlined above. Theelectroplated film was put in an etching solution containing 0.1 MNa₂S₂O₃/0.01 M K₃Fe(CN)₆/0.001 M K₄Fe(CN)₆ for ˜1 min to remove the goldparticles reduced by the gelatin in the non-patterned area. This etchingstep is preferred to make the film more transparent to UV during thepatterning of photoresist. The film was immobilized on a glass slideusing cellophane tape. SU-8 photoresist was spincoated directly onto thefilm at 500 rpm for 20 s. The film was baked at 95° C. for ˜10 hours,followed by exposure from the bottom for 7.5 min (10 mJ·cm⁻²·S⁻¹ at 405nm) with a Karl Zeiss MJB3 contact aligner and post-baking at 90° C. for˜10 min. The photoresist was developed in PGMEA for ˜4 hours withmagnetic stirring. Finally, through mask electroplating of the filmcarrying the patterned photoresist in a nickel electroplating bath wasperformed for ˜150 hours while maintaining a current of 10 mA.

[0049] The fact that the film served as the substrate and the fact thatthe metallic structures on the film not only served as the mask in thephotolithographic step, but also as the cathode in the electroplatingprocedure reduce the number of steps significantly compared toconventional processes for the fabrication of high aspect ratio metallicstructures. We obtained a negative Poisson ratio structure (Xu, B.;Arias, F.; Brittain, S. T.; Zhao, X.-M.; Grzybowski, B.; Torquato, S.;Whitesides, G. M. Adv Mater. in press 1999) with a maximum aspect ratioof 5 (FIG. 8b).

[0050] Those skilled in the art would readily appreciate that allparameters and configurations described herein are meant to be exemplaryand that actual parameters and configurations will depend upon thespecific application for which the systems and methods of the presentinvention are used. Those skilled in the art will recognize, or be ableto ascertain using no more than routine experimentation, manyequivalents to the specific embodiments of the invention describedherein. It is, therefore, to be understood that the foregoingembodiments are presented by way of example only and that, within thescope of the appended claims and equivalents thereto, the invention maybe practiced otherwise than as specifically described. The presentinvention is directed to each individual feature, system, or methoddescribed herein. In addition, any combination of two or more suchfeatures, systems or methods, provided that such features, systems, ormethods are not mutually inconsistent, is included within the scope ofthe present invention.

What is claimed:
 1. A method of forming a conductive pattern,comprising: providing an article including a metal atom precursorcapable of conversion to elemental metal; disproportionately exposing afirst portion of the article to electromagnetic radiation at a levelgreater than exposure at a second portion of the article, in an amountand for a period of time sufficient to convert at least some of theprecursor at one of the portions to elemental metal at a conversionlevel greater than conversion of precursor to elemental metal at theother portion; and depositing metal, from a source external of the metalatom precursor, proximate the portion of the article including metalatom precursor converted at a greater conversion level in an amountgreater than deposition of metal at the other portion.
 2. A method as inclaim 1, wherein the metal atom precursor is a metal salt.
 3. The methodof claim 2 wherein the metal salt is a silver halide.
 4. The method ofclaim I wherein the metal deposited from the source external of themetal atom precursor is deposited using electroless deposition.
 5. Themethod of claim 1 wherein the article comprises photographic film. 6.The method of claim I wherein the planar dimension of a portion of theconductive pattern is less than about 100 μm in width.
 7. The method ofclaim 6 wherein the planar dimension of a portion of the conductivepattern is less than about 50 μm in width.
 8. The method of claim 7wherein the planar dimension of a portion of the conductive pattern isabout 30 μm in width.
 9. The method of claim 1 further comprisingfreeing the metal from the article.
 10. The method as in claim 1,wherein the metal is deposited proximate the first portion whileessentially no metal is deposited proximate the second portion.
 11. Themethod as in claim 10 wherein the metal is deposited in an amountsufficient to provide conductivity to the first portion.
 12. The methodas in claim 10 further comprising electroplating a metal onto the firstportion.
 13. The method as in claim 1, wherein the metal is depositedproximate the second portion while essentially no metal is depositedproximate the first portion.
 14. The method as in claim 13 wherein themetal is deposited in an amount sufficient to provide conductivity tothe second portion.
 15. The method as in claim 13 further comprisingelectroplating a metal onto the second portion.
 16. A method comprising:deforming a flexible metal structure from a first configuration to asecond configuration; and depositing auxiliary metal on the metalstructure to the extent that the structure is self-supporting in thesecond configuration.
 17. The method of claim 16 wherein the flexiblemetal structure is disposed on photographic film.
 18. The method ofclaim 17 further comprising freeing the structure from the photographicfilm.
 19. A method comprising: exposing photoresist to electromagneticradiation through a metal mask; developing the photoresist therebyforming a photoresist pattern; directing a metal deposition compositionto the metal mask via the photoresist pattern; and depositing auxiliarymetal on the metal mask from the deposition composition.
 20. The methodof claim 19 wherein the metal mask is produced by selectively exposingportions of the mask to electromagnetic radiation and adding metal tothe same or to alternate portions of the mask using electrolessdeposition.
 21. The method of claim 19 wherein the auxiliary metal isdeposited via electroplating.
 22. The method of claim 19 wherein themetal is in the form of a pattern and at least a portion of the patternhas an aspect ratio of greater than or equal to about
 5. 23. A method offorming a conductive pattern, comprising: illuminating a photographicfilm with a desired illumination configuration; developing thephotographic film so that illuminated or non-illuminated portions of thefilm are adjusted to be in an altered state; and selectively depositingadditional conductive material onto portions of the film in an alteredstate in amounts greater than amounts of conductive material depositedon portions of the film not in the altered state.
 24. The method ofclaim 23 wherein the additional conductive material is deposited viaelectroless deposition.
 25. The method of claim 24 further comprisingelectroplating additional metal on the metal deposited via theelectroless deposition.
 26. The method of claim 23 wherein theconductive pattern is a circuit.
 27. A method of forming a discontinuousmetallic structure comprising: illuminating a photographic film with adesired structure configuration; developing the photographic film sothat illuminated or non-illuminated portions of the film are adjusted tobe in an altered state; and selectively depositing additional conductivematerial onto portions of the film in an altered state in amountsgreater than amounts of conductive material deposited on portions of thefilm not in the altered state.
 28. The method of claim 27 wherein theadditional conductive material is deposited via electroless deposition.29. The method of claim 28 wherein the additional conductive material isnickel.